The warning comes amid international outrage over the Syrian regime's alleged use of chemical weapons against its own people.

"We believe there has been a chemical weapons connection between North Korea and Syria," Defence Ministry spokesman Kim Min-Seok said.

Any link between North Korea and the attacks in Syria could further isolate Pyongyang, which is prohibited from international sales of its weapons under UN sanctions for conducting nuclear and missile tests.

Suspicions over chemical weapons trade between Pyongyang and Damascus have been raised in the past. Concerns have grown since South Korea intercepted a North Korean shipment of protective gear on a vessel sailing near the southern port of Busan in 2009, Kim said.

Later that year Greece also seized almost 14,000 suits that provide protection from chemical weapons on a North Korean ship they believed was headed to Syria.

Japan's Sankei Shimbun newspaper reported last month that North Korea tried to export gas masks to Syria this spring. Acting on the tip from the United States, Turkey intercepted a vessel carrying rifles, pistols, ammunition and gas masks, it said.

The North is believed to have up to 5,000 tons of chemical weapons deliverable by artillery or missile, Kim said.

South Korea supports international sanctions against Syria because the regime's use of chemical weapons, if confirmed, could give the wrong signal to North Korea, he said.

A report by a UN Security Council panel of experts said that in June that Pyongyang had continued to import and export items relevant to missile and nuclear programmes.